PURPOSE

Muscle hypertrophy is likely to result from the cumulative effects of repeated bouts of resistance exercise (RE) on postexercise molecular responses. Therefore, we determined muscle growth- and regeneration-related mRNA expression in response to a single RE bout both before and after a strength-training (ST) period. By means of this novel longitudinal setting, we examined whether postexercise gene expression at the transcriptional level is different in the trained and untrained state.

METHODS

Eleven untrained healthy older men and 11 controls (age 62.3 +/- 6.3 yr) volunteered as subjects. Muscle biopsies from the vastus lateralis muscle were taken at rest and 1 and 48 h after five sets of 10-repetition leg press RE both before and after 21 wk of supervised ST.

RESULTS

Myostatin and myogenin mRNA expression, determined by real-time RT-PCR, increased (P < 0.05) after ST. Conversely, the single RE bout decreased myostatin mRNA after ST, with the decrease showing a negative correlation (r = -0.65, P < 0.05) with the long-term increase in myostatin during ST. Furthermore, RE before ST increased myogenin mRNA (P < 0.05) and tended to increase after ST (P = 0.08). Myostatin receptor activin IIb mRNA levels were decreased at 1 h after RE in the pre-ST condition (P = 0.05) and also tended to decrease in the post-ST condition (P = 0.07). RE-induced downregulation in myostatin mRNA correlated with the ST-induced increase in total body muscle mass (r = -0.82, P = 0.002).

CONCLUSIONS

A single bout of RE in older men can downregulate the expression of myostatin receptor activin IIb mRNA. ST influences the response of myostatin to RE, as short-term RE-induced downregulation of myostatin was observed only after ST. The results also indicate that RE-induced alterations in myostatin mRNA expression may have a role in ST-induced muscle hypertrophy.